1. Field of the Invention
The present invention relates to blow molding machines of the extrusion-blow type, and more particularly to an extrusion-blow-type blow molding machine in which the extruder and the extrusion head are mounted on a carriage for movement toward and away from a molding station to permit improved access to the extruder, to the extrusion head, and to the blow molds.
2. Description of the Related Art
Extrusion blow molding machines generally include a horizontally-disposed extruder having a rotatable screw positioned within a tubular barrel. Plastics material in pelletized or particulate form is introduced into the barrel at one end thereof and is carried by the screw along the barrel to an outlet end. As the material is transported within the barrel it is mechanically worked to increase its temperature, thereby softening the material. External heat is also applied to the barrel to accelerate the softening process so that the originally discrete particles or pellets combine to form a viscous mass that can be continuously extruded through an extrusion die.
After the particulate material has been sufficiently heated and the particles have coalesced into a coherent, viscous mass, the heated, viscous material is forced through the extruder outlet to a suitable extrusion head, which includes the extrusion die, for extruding a tubular length of heated plastic material called a parison. The parison can be of either uniform or variable cross section, depending upon the type and shape of article to be blow molded.
The extrusion head is generally positioned above a horizontally separable, cooled blow mold so that the extrusion die opening is located above and between the halves of the blow mold when the mold is open. As the parison issues vertically downwardly from the extrusion head it is positioned between the two mold halves, which together define a cavity in the shape of the article to be blown.
The molds are closed about the parison with the upper and lower portions of the molds clamping the parison. Pressurized air is introduced into the parison, to blow the parison outwardly and expand it so that it contacts the interior surfaces of the mold to cool and thereby provide a thin-wall, hollow article, such as a container, or the like.
When access is required to the extrusion head for maintenance, cleaning, or perhaps for the substitution of one extrusion head for another, it is often inconvenient to service the machine because the extrusion head is not easily accessible. Either the head is in a fixed position above the molds and the mold clamping and blowing station, with the associated mold hardware impeding access to the extrusion head and extruder outlet, or, if the head is movable, its movement is limited to a point above another portion of the machine.
One approach that has been proposed to facilitate access to an extrusion head of a blow molding machine is disclosed in U.S. Pat. No. 3,491,404, which issued Jan. 27, 1970, to Gottfried Mehnert. The blow molding machine described in that patent includes a horizontally positioned rail along which the extrusion head can be carried by means of a trolley arrangement that rides along the rail. However, the axis of the extruder is perpendicular to the vertical plane in which the rail axis lies, and thus disconnection of the extruder head from the extruder is required in order to effect servicing.
Another arrangement for shifting the position of an extrusion head is disclosed in U.S. Pat. No. 3,837,780, which issued on Sep. 24, 1974, to Paul G. Strong. However, the Strong device contemplates shifting movement of an extrusion head between each of two side-by-side molds but within the confines of a generally rectangular machine frame.
It is an object of the present invention to overcome the deficiencies of the prior art devices, and to provide an improved extrusion blow molding machine wherein unimpeded access to the extrusion head is facilitated for cleaning and servicing.
It is another object of the present invention to provide an extrusion blow molding machine in which the extruder and extrusion head are carried for joint movement along the frame to and from respective servicing positions.